Drilling rigs fitted with top drives rotate suspended pipe strings while the pipe strings are being inserted into well bores. CRT elements have pipe gripping and pipe manipulating features that are operated by fluid powered apparatus. Such fluid powered apparatus is usually powered and controlled by consoles on the rig floor. The consoles are stationary and the controlled apparatus, at least in part, is often rotated. A swivel arrangement is used to allow the transfer of fluid power from the stationary to the rotating elements.
The diameter of the necessary fluid seals involved, and the rotational speed, tends to tax the seals durability. Such seals tend to have short service life and seal failures are a persistent problem.
Fluid power is used, by the CRT, to manipulate the pipe and pipe handling gear while the pipe string is not rotating. Fluid power is also used to secure the pipe string to the CRT during rotation.
To improve reliability, the design of CRT equipment benefits from the separation of fluid powered features that operate during non-rotating activity from the features that operate during pipe string rotation. That separation supports the use of accumulators to provide fluid power during pipe string rotation for securing the pipe string to the CRT, for instance. While the CRT is not rotating, fluid power can proceed through the swivel to charge the accumulators. After the accumulators are charged, and before rotation, the fluid power can be reduced to reduce the challenge to the seals in the swivel. That still leaves the seals in sliding contact. There is still a need to better protect the seals. This invention addresses the need to further protect the swivel seals.